Gas lift plunger



P 14, 1954 R. P. VINCENT ETAL 2,688,928

GAS LIFT PLUNGER Filed April 28, 1950 ez F 6l //5Q H V H 63 I m 1 b l2 FIG. 3

FIG. 1 FIG. 2 INVENTORS RENIC P. VINCENT ATTORNEY Patented Sept. 14, 1954 GAS LIFT PLUNGER Renic P. Vincent, Tulsa, Okla, and Benjamin J. Rhoads', Jr., Brownfield, Tex., assignors to Stanolind Oil and Gas Company, Tulsa, Okla;, a corporation of Delaware Application April 28, 1950, Serial No. 158,836

This invention pertains to an apparatus for artifically producing wells. More particularly, this invention pertains to an improved plunger for use in gas lifting oil wells.

In gas lifting liquid from a well, the common practice has been to inject gas by any of a number of means into an education tube below the level of the fluid, thereby raising the liquid level to the surface either by aeration of the column of liquid in the eduction tubing or by mere displacement of slugs of liquid with the gas. As is well known, by either method the efiiciency of the process is generally lower than that of other means of artificial lift and, therefore, gas lift operations in many wells-particularly stripper or marginal wells-is not justified.

It has been proposed to improve this efficiency of gas lift by inserting a divider means, such as a plunger, between the liquid column and the gas column which is used to lift the liquid column to the surface. By this means by-passing of liquid with the gas is avoided, and the gas/liquid ratio is substantially reduced. Although various modifications and improvements have been made in that system of gas lifting wells, it has not been widely used due to the high installation cost. We have found that in that system the clearance between the plunger and the tubing must be very low to prevent the gas from by-passing the plunger and that, in order to maintain this clearance in the proper range, a specially bored or selected tubing string is required. The cost of special boring is often prohibitive, in the first place; and, second, the possibility of injury, such as denting of the tubing string during handling, is rather high. Wells requiring artificial lift generally will not justify such expense and such risk. While it would be possible occasionally to select tubing joints having a substantially uniform diameter, for a special string, obviously, no oil producer could afford to buy tubing, select joints therefrom, and sell or salvage the remainder of the joints. Even with selected joints, however, the efliciency of a plunger gas lift system using a fixed diameter plunger is reduced by even minor variations in the inside diameter of the tubing. Such variation cannot be avoided in a long tubing string. Since the fixed diameter plunger must be small enough to pass the smallest diameter in the complete tubing string, it invariably allows gas by-passing at the larger points in the string. These difiiculties have substantially limited the use of the plunger gas lift system.

It is therefore an object of this invention to provide an improved apparatus for gas lifting 6 Claims. (Cl. 103-52) wells. It is a further object of this invention to provide an improved gas lift plunger. A still further object of this invention is to provide a gas lift plunger which will prevent by-passing of fluid in tubing having random variations in diameter. It is another object of this invention to provide a gas lift plunger which is expanded in the tubing by the overlying fluid head and contracted when that head is discharged from the tubing at the wellhead. These and other objects of this invention will become apparent from the following description of certain embodiments of our invention which are presented for the purpose of illustration. In this description, reference will be made to the accompanying drawings in which:

Figure 1 is a diagrammatic cross-sectional view of a gas lift system adapted to use a plunger of our. design;

Figure 2 is a cross-sectional view of a diagrammatic representation of one embodiment of our improved gas lift plunger; and

Figure 3 is a cross-sectional view of a preferred embodiment of our improved gas lift plunger.

Our gas lift plunger, in brief, comprises a tubing swab which is expanded near the bottom of a well whenever a predetermined amount of fluid head accumulates in the tubing above the swab or plunger. This expanded plunger, together with its load of liquid, may be raised to the surface with gas produced by the well, or with gas injected from an external supply, the expanded plunger preventing'by-passing of the gas and intermingling of the gas and liquid as the liquid is raised through the tubing. When the liquid load above the plunger is delivered to the surface and displaced into the flow line from the well, the

plunger-due to the decrease in the pressure in the tubingis contracted automatically, allowing it to fall through the tubing and commence another cycle.

Referring now to Figure 1 the tubing I0 is shown in position within a gas lift well having a casing I I. The annular space between the tubing and casing is sealed near the bottom of the well by a packer I2 whereby the gas used to lift the oil does not come in contact with the producing formations below the packer. A standing valve l t is located in the tubing near the bottom of the well, preferably at a point below the producing fluid level of the well. Above the standing valve a solid plug [4 is suitably fixed as by welding into the tubing to prevent fluid flow through the tubing, and to cause well production entering the tubing to flow through lower perforations l-5, bypass !6, and upper perforations .I 1'. By this means when the plunger I8 comes to rest on bottom stop l9, and when it expands, and seals the tubing, oil may continue to flow into the tubing above the plunger. Gas lift valves 2| are spaced along the tubing in the annular space between the tubing and casing with the bottom gas lift valve located below the plunger seat I9 and above plug l4. Any number of gas lift valves may be used along the tubing for the purpose of unloading the tubing when it becomes filled with liquid. The spacing of these valves, as is well known in the art, is adjusted such that the available gas pressure will overcome the maximum fluid head above any gas lift valve. In a preferred embodiment the gas lift valves are actuated by the pressure of the gas in the annular space between the tubing and the casing, the bottom valve being actuated by a pressure substantially less than the pressure required to actuate any of the upper valves. Thus; the tubing may be unloaded when it beomes filled with liquidzby; application ofphighpressure, for example, a pressure-in :thC" range of .about 500- 1000 p. s. i; It is desirablethattheupper gas lift valves be actuated :at progressively decreasing pressures starting tat-the'.top. Thus, when the liquid has been discharged from :the tubing above the top gas lift valve the pressure of the gas in the annulus can be reduced to. below the opening pressure for the top gas lifta-valve, thereby selectively closing that valve and displacing the liquid inthe tubing between thefirst and second gas lift valves.- All the gas lift valves areactuated in this manner by controlof the-gas pressure in the annular space to unload the tubing. Thebottom gas lift valve preferably operatesat a pressure substantially lowerthan-any other valve in-the system, for example, at a pressure of about 100 to 300 p. s. i., so that a wide range of gas pressures is available for actuating the plunger operating gas lift valve. 1

At the surface the space between tubing l and easing l is sealed. by: aztubing head ,22 containing a gas inlet opening 23. A: full-opening control valve 24' mayabezplaced'on the upper end of the tubing in accordance. with the customary practice in this art. Above this: valve we provide means to trap the plunger when it is considered desirable; and means to discharge fluid from the tubing without permitting the plunger to escape. In this connection a trapping device 25 containing a'movable cross pin 26 vis fixed to the tubing'and arrangedso that when the plunger is in the upper end of the tubing at the end of its power:,.stroke the movable cross pin may be inserted through hole 21 into the tubing to prevent. the plunger from falling by gravity down the "tubing when" the'force' of the lifting gas has been "dissipated to the flow line. Liquid above the plunger isdischarged through perforations 28 into a jacket 29. From this jacket the well fluids and the lifting gas are discharged through opening 3| into the flow line from the well. The section of tubing 32 above perforations 28 may be plugged and used as a pneumatic cushion for the plunger. In some cases it may be desirable to provide in this section a resilient material such as rubber or a spring to cushion the shock on the plunger when itis lifted to the surface on the power stroke at high velocity.

Turning now to a detailed description of the plunger, Figure 2 shows the elements of one type of gas lift plunger which is adapted to be expanded by the pressure in the tubing. In this embodiment, a variable volume pressure chamber '40 is disposed in a body or tubulaimandrel 4| which is closed at both ends. At one end, preferably the upper end when the plunger is inserted in the tubing, a piston 42 is fitted over the end of the mandrel 4| and adapted. to move axially over the mandrel, whereby the volume of the pressure chamber may be varied substantially. At the lower end of the piston a packing gland 43 may be provided toseal the pressure chamber 48 and prevent fluid by-passing between the piston and the mandrel. At the other end of the mandrel a head 44 is suitably afiixed, as by threads 45, to the mandrel to seal the lower end of the pressure chamber. This head may have'a filling port 46 containing a. valve 41 whereby the pressure chamber may be prepressured at the surface as hereinafter described.

A plug 48 threaded into the filling port is sometimes desirable to seal the pressure chamber and prevent well fluids from entering this chamber when the external pressure. in the well is greater than the pressure in pressure chamber 3411. A resilient packer 50, constructed of synthetic rub.- ber or other material which will not deteriorate in the'well, provides the sealing element which prevents the lifting gas from bypassing: the plunger on the power stroke. This packer is vulcanized at the upperaend to the packing gland nut 5| which is affixed to and moves'with piston 42. The packer 50 is vulcanized at the lower' end to'fiange 52 which'maybea part or extensions of head 44. The'packerotherwise fits loosely on mandrel 4|, so th'at-it is compressed when piston 42 moves down on mandrel" 4|. Similarly, the packer is'exte'nded" when the piston moves up on mandrel 4|. IAsQthe length ofthe packer 5!! is compressed and extended by 'pressure variations in thet-ubinggits external diameter is respectively expanded and contracted.

Thus the external diameterof the packer ill is controlled by'the external pressure 'on' the plunger, the diameter increasing as the pressure increases and decreasing as the pressure decreases.

In operation the plunger is assembled as indicated, and the pressurechamber 40 is'p'repressured to any desiredpressure -thispressurede pending upon a number of elements, including the resilience of packer 50, the length of pressure chamber' lfl, and theamoun't of fluid to'be lifted from the wellper cycle 'of the plunger. In general, we have found that in 2 /2 inch tubing 1 barrel of oil above the plunger produces a pressure of about p. s. i. Therefore, if it is desirable to lift 1- barrel of oil'per cycle, the pressure within pressure'cha'mber 40 should be adjusted by removing plug 68 in head M andinjecting, for example; air through fillingport 46 and valve 41. The pressure within the chamber should be adjusted'so that, when external pressure of about'70 p. s. .i. is applied to the plunger, the external diameter of packer 50 is slightly greater than the internal diameter of 2 /2 inch tubing. When the pressure is thus adjusted, the chamber is sealed with plug 48 and the plunger is dropped into the tubing, preferably with head 44 atthe lower end. However, the plunger operates satisfactorily when it is inserted with the piston at the lower end.- With the picker 5|! elongated dueto the gas pressure within pressure chamber '40, its external diameter is substantially smallerthan the internal diameter ,of the tubing; and, therefore, the plunger. falls relatively, freely through the tubing. At the lower ;end1;of'. .th,e, tubing-:the

into gas inlet opening 23.

'on each well.

plunger'strikes the liquid before it reaches ithe the fall and prevent injury to the plunger. The

plunger then rests on the bottom stop within the tubing, and fluid by-passes between the tubing and the packer as the well and tubing .fill with fluid. When the fluid head on the plunger is equal to the presetpressure at which the external diameter of packer 50 is equal to the internal diameter of thetubing, the plunger seals the tubing but the fluid level in the tub:- ing continues to rise. The plunger may be raised by the gas production from the well by leaving out plug I4, lower perforations I5, by-pzass l6, and upper perforations I! but I havefound it generally desirable to inject gas as described above below the plunger and lift it, together with the liquid load, to the surface. Gas injection at a pressure suflicient only to actuate the bottom gas lift valve is injected intermittently The amount of gas injected and the frequency of the injections is :governed by well productivity, gas pressure, and.

the like which are determined experimentally As the plunger rises in the tubing, the packer 50, being of resilient material,

expands and contracts adapting itself to variations in the tubing diameter and preventing gas from by-passing the plunger. At the surface the liquid above the plunger is discharged from the tubing into the flow line, a tank, or the like as described above. As this fluid is displaced from the tubing, gas injection is stopped and the .pressure of the power fluid which lifted the plunger to the surface is dissipated, the plunger again elongates, the external diameter of the packer contracts, and the plunger falls relatively freely to the bottom of the tubing where another cycle is commenced. I

While the embodiment above described contains all the necessary elements of a fluid-actuated automatic gas lift swab or plunger, the embodiment shown in Figure 3 is preferred. this embodiment, as in the embodiment shown in Figure 2, the external diameter of packer 5B is controlled by the hydraulic pressure on the plunger. The sealing element or packer is affixed at the lower end to a mandrel 6|. The packer may be vulcanized to the mandrel but, in some cases, it is desirable to compress the cylindrical ends between metallic conical adapters 62 and 63 as indicated-the adapters then being mounted on the mandrel. Theupper adapter '62 is affixed to and is a part of the plunger body The lower adapter is aflixed to the lower end of mandrel 6| and moves axially of the body 64 with mandrel Bl. As in the above-described embodiment, the plunger contains a variable volume pressure chamber 40 which, as hereinafter described, may be filled at the surface with a gas, such as air, or with a liquid and a gas. The pressure chamber contains a head 44 which is connected, as by threads 45, to the body 64.

.A filling port 46, valve 41, and plug 48 are also provided in this head to fill and seal the pressure chamber.

Mandrel 6|, which is open at the bottom to permit fluid pressure from the well to be applied against mandrel head 66, is moved axially within body 64 to extend and compress packer 50'. The pressure chamber is sealed at the lowerencl be- Inv tween-body filandimandrel 6hr A stuffinggland may be provided, but, due. to thevarlation in frictional resistance of such glands, a bellows 6! is preferred-the bellows'being connected at the upper endto mandrel head 66 and at the lower end to the body via upper adapter 62. l

I In some cases, to avoid injury to bellows 61, a partition 68 may be provided in body 64. This partition contains an axial bore 69 and an annular valve seat 10. The pressure chamber 40 may be divided to produce a second chamber II when extreme pressures are applied to the plunger. Thus, a high pressure causes the mandrel to raise and valve 12 to contact seat 10. Injury to the bellows is thus prevented by filling pressure chamber 40 up to partition 68 (lower pressure chamber 1|) with liquid-the remainder of the pressure chamber being filled with a gas such as air. When pressure is applied to mandrel head 66 by the well fluids, the mandrel moves into the body, compressing packer 50 and extending bellows 61. At an extreme pressure, i. e., a pressure substantially above operating pressure, valve 12 eventually seats on valve seat 10, limiting this axial movement and extension of bellows 61. Should the external hydraulic pressure he further increased, injury to the bellows is prevented,

' sure chamber 40 and the well pressure within mandrel 6|, extension and expansion of bellows 61 is prevented after valve 72 is closed. As in the embodiment described in Figure 2, axial movement of the mandrel relative to body 64 extends and compresses packer 50 and simultaneously contracts and expands respectively the external diameter of the packer.

In operation, the pressure chamber 40 is prepressured by injecting liquid and gas through filling port 46. Liquid is first injected into the pressure chamber until the liquid level is substantially at the level of partition 68. Gas, such 1 as air, is then injected until a predetermined pressure is reached. At the correct pressure, which may be from substantially zero to a hundred pounds or more, depending upon several variables, the packer, if placed under an external hydraulic pressure equal to the fluid head to be lifted on each cycle, expands to substantially the internal diameter of the tubing. The plunger is then inserted into the tubing and allowed to fall until the preset hydrostatic pressure is reached or until the plunger strikes bottom stop I 9. The

packer then remains extended until the predetermined static head is reached, at which time packerill is compressed axially by movement of mandrel 6| upward in body '64. As the packer is thus compressed, its external diameter is expanded, resiliently sealing the space between the plunger and the tubing. Further production of the well prior to gas injection merely increased the force exerted by the packer on the tubing. Since neither gas nor liquid will by-pass the plunger, it will be lifted to thesurface when gas is introduced below the plunger by the bottom or plunger-operating gas lift valve. The external diameter of packer 50 remains expanded as the plunger. is driven through the tubing on the power stroke, dividing the liquid and gas, preventing gas from by-passing the plunger and thus reducing the gas/liquid ratio. As liquid is discharged from the tubing and the lifting gas pressure is dissipated, mandrel BI is driven out of body 64 by the expanding gas in pressure chamber 40,

the injection of gas.

elongating packer 50 and reducing its external diameter. When this external diameter is substantially reduced, the plunger falls relatively freely on the return stroke to the bottom of the well, and another cycle is commenced.

mechanism at the surface, it may be injected by use of an intermitter valve actuated by liquid head in the tubing, it maybe injected by a bot- 1 tom-hole valve actuated from the surface, or the like. This invention is therefore not limited by the method or apparatus used to inject gas, to

shut off gas, or the like. Furthermore, various modifications of other auxiliary apparatus such as tubing packers, formation packers, gas lift valves, and the like, can be applied to our improved gas lift plunger without departing from the spirit thereof.

The inventionv should, therefore, not be construed to be limited by the above description, which is presented merely for the purpose of illustration, but should be construed in light of the appended claims.

We claim:

1. A plunger for lifting well fluids from wells through tubing with gas under pressure comprising a hollow body, a mandrel movable axially in said body, an expansible bellows sealed at one end to said body and at the other end to said mandrel and forming with said body and said mandrel a hermetically sealed pressure chamber having a volume which tends to vary in inverse proportion to the external fluid pressure on said plunger, a cylindrical resilient packer attached at one end of said body and adapted to expand diametrically when compressed axially, and means operatively connecting the otherend of said packer to said mandrel to compress said packer axially when said external fluid pressure is high and to extend said packer axially when said external fluid pressure is low.

2. A plunger according to claim 1 including means to pre-pressure said pressure chamber to a pressure greater than the external pressure on said plunger, I

3. A gas lift plunger for lifting well fluids comprising a cylindrical body, a pressure head at the upper end of said cylindrical body, a cylindrical resilient packer connected at the upper end to the lower end of said body, a mandrel extending through said cylindrical packer and into said body, the lower end of said cylindrical packer being connected to said mandrel, a flexible sealing element connecting said mandrel and said body and forming a hermetically sealed pressure chamber within said body, a partition in said pressure chamber forming upper and lower compartments, said flexible seal being located in said lower compartment, and a valve in said partition actuated by the movement of said mandrel for preventing fluid flow between said upper and said lower compartments whereby when said lower compartment is filled with a relatively incompressible fluid and said upper compartment is filled with a relatively compressible fluid and when a high fluid pressure is exerted on said element said mandrel will move into said pressure chamber, close said valve, and thereby protect said flexible element from destruction.

4.'In a gas lift plunger for raising liquids through a tubing comprising a body, a pressure chamber within said body having a movable head which is adapted to vary the volume of said pressure chamber in inverse proportion to the external fluid pressure on said plunger, a cylindrical resilient packer connected at one end to said body, and means operatively connecting the other end of said packer to said movable head to compress said packer axially when said external fluid pressure is high and to extend said packer axially when said external fluid pressure is low, the improvement comprising flexible seal means between said body and said movable head to hermetically seal said movable head in said pressure chamber whereby external fluids cannot enter said pressure chamber and said plunger will operate under varying pressure conditions over an extended period of time.

5. A plunger for lifting well fluidsfrom wells through tubing with gas under pressure comprising a hollow body, a mandrel movable axially in said body, an expansi-ble bellows sealed at the ends to said body and to said mandrel respectively and forming with said body and said mandrel a hermetically sealed pressure chamber within said body, a partition within said pressure chamber forming upper and lower compartments, said bellows being disposed in said lower compartment, a valve between said upper and said lower compartments actuated by the movement of said mandrel relative to said body to prevent fluid communication between said upper and said lower compartments when said plunger is subjected to high fluid pressure so that when said lower compartment is filled with a relatively incompressible fluid and said upper compartment is filled with'a relatively compressible fluid said valve will close, separating said upper compartment from said lower compartment to protect said bellows from destruction, and a cylindrical resilient packer disposed on said mandrel with one end of said packer being connected to said mandrel and the other end of said packer being connected to said body, said mandrel being forced into said body, decreasing the volume of said pressure chamber and increasing the external diameter of said packer when the fluid pressure on said plunger is increased and the volume of said pressure chamber being increased and said diameter being decreased when the pressure on said plunger is decreased, whereby the motion of said mandrel relative to said body will expand said packer and seal said tubing when the fluid head above said plunger reaches a predetermined amount, said plunger will be displaced through said tubing to the surface carrying said well fluids when said gas is injected into said tubing below said plunger and whereby the diameter of said packer will be decreased when the pressure on said plunger decreases, allowing said plunger to fall relatively freely through said tubing when said well fluids have been displaced through said tubing to the surface.

6. A plunger for lifting well fluids from wells through tubing with gas under pressure comprising a hollow body, a mandrel movable axially in said body, an expansible bellows sealed at one end to said body and at the other end to said mandrel and'forming with said body and said mandrel a hermetically sealed pressure chamber within said body, and a cylindrical resilient packer disposed on said mandrel with one end of said packer being connected to said mandrel and the other end of said packer being connected to said body, said mandrel being forced into said body, decreasing the volume of said pressure chamber and increasing the external diameter of said packer when the fluid pressure on said plunger is increased and the volume of said pressure chamber being increased and said diameter being decreased when the pressure on said plunger is decreased, whereby the motion of said mandrel relative to said body will expand said packer and seal said tubing when the fluid headabove said plunger reaches a predetermined amount, said plunger will be displaced through said tubing to the surface carrying said well fluids when said gas is injected into said tubing below said plunger and whereby the diameter of said packer will be decreased when the pressure on said plunger decreases, allowing said plunger to fall relatively freely through said tubing when said well fluids have been displaced through said tubing to the surface.

0 References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 971,612 Holliday Oct. 4, 1910 10 1,485,248 Carpenter Feb. 26, 1924 1,846,000 Fletcher Feb. 16, 1932 2,486,617 Soberg Nov. 1, 1949 2,508,174 Knox et al May 16, 1950 2,527,929 Hebard Oct. 31, 1950 15 2,555,112 Brown May 29, 1951 

